Prior art microwave ovens have generally included a mechanical timer in the form of a presettable timer which is rotated to the proper position by the user to set the oven timer so that it measures the proper interval. Although satisfactory in many respects, the mechanical timers have a number of drawbacks. For instance, mechanical timers for microwave ovens are required to be highly accurate and as a result are costly. In fact, some microwave ovens have used two mechanical timers, one for relatively short time intervals and the other for relatively long time intervals, in order to ensure the accuracy needed to time a microwave oven cooking interval. Other microwave ovens have included a push button actuated timing unit in which there are a plurality of push buttons, each representing a specific time interval. With this type of timer, the user cannot select certain time intervals because each push button usually represents a time interval which is five or ten seconds greater than the next shorter time interval.
It has been known in the past to provide an appliance with a digital logic control system. An example of such a system is shown in U.S. Pat. No. 3,819,906, which discloses a digital logic control system for an electric range. This control system not only provides a timing function for the oven and surface heating elements but also provides a time of day clock and a timer as well. Normally, the time of day is displayed on a display which also displays the information stored in the digital logic control. Although this system is satisfactory in many respects, the amount of digital logic required to implement this system is cumbersome and requires a large amount of area on an integrated circuit, and thus is relatively expensive. In addition, this control system does not allow two stage programmability where the same operating element is cycled through two stages of operation, the duration of each stage being determined by the user.